This hasn't been a good week for those thinking of hiring a nanny. First, Devil's Advocate (BBC1) raised the possibility that your little darlings might be flambeed by a witch (never mind that she wasn't a witch and nobody got flambeed anyway; th e guilty parent is given to dire imaginings). Then, just as you were calming down, Tears before Bedtime (BBC2) turns up, a grimly watchable lampoon on the agonies of the career couple.

Given that questions of elitism and populism are in the air, it's possible to wonder quite how closely this will touch that part of the audience that doesn't spend time fretting about whether to give nanny the master bedroom. Indeed, it's possible the conspicuous prosperity of everyone on screen (most London viewers will be able to price those period features, that enviably spacious garden) may even alienate some of the programme's natural constituents. This won't look uncomfortably close to the truth for many people, more like jolly comfortably distant from it.

Still, schadenfreude may carry the day even if fellow feeling doesn't. And Sandy Welch's script shakes off the claims of naturalism anyway, with some concertedly comic exaggerations. It may be that she has anecdotal evidence for the opening incident, in which a surreptitious pavement auction takes place, as a nanny marshalls the bids from the upstairs window of her current employer's house. But elsewhere the plot is clearly mischievous, turning up the volume on parental disquiets until a ludicrous distortion results. "Before you come in, you've got to understand - my children are ugly and disgusting," says a weeping mother, abjectly surrendering to the fact that nanny has the whip hand. This isn't acted as a wry command of the situation but genuine distress.

The old warfare between upstairs and downstairs is complicated by the fact that we're all supposed to live in a bungalow now. The Baylises soon discover their dream applicant - the one who's happy to do the ironing - is actually a nightmare, a hygiene psychotic who fills the night with the throb of the tumble-dryer. Her replacement is even more threatening - pretty enough to make the wife decidedly twitchy. This is all gleefully observed, but you have to hope the glee won't get out of hand - there's alr eady something a little chilly about the unremitting sourness of the thing, the way that any generosity of spirit is stamped on in short order.

The Last Machine (BBC2), a cultural history about the early days of cinema, is a real treat - a documentary whose playfulness is never at odds with its ideas. It has impeccable manners, too, because while its more arcane jokes will greatly enrich the programme for viewers who get them, they are so modestly presented that they won't snub the rest. Besides, there are abundant pleasures in the basic material assembled here. This is cinema in its first flush of wonder, when the content barely mattered - theJurassic Park of 1896 was a film called Leaving Amberieu Station, and for several years titles continued to serve as a plot synopsis: How It Feels to be Run Over along with Demolition of a Wall were both big box-office successes.

Ian Christie's script (nicely delivered by Terry Gilliam) made a fascinating case for the odd symbiosis between the railways and early film, two inventions that transformed the modern sensibility. Its fancy-dress is wonderfully suggestive, too, as when Mr Toad and Marinetti, the Italian writer, sit side-by-side in a motor car, a witty joke about the Futurist infatuation with machinery. Elsewhere, even the soundtrack helps the argument along - a time-lapse film about the demolition of a building is accom panied by Victorian pianola, which sounds oddly like Philip Glass. The medium was barely 10 years old and somebody had already made Koyaanisqatsi.